INTERCONNECT project : Bioaccumulation of organometallic compounds in Tropical Chains

**Influences of INTERCONNECTIONS between terrestrial and aquatic environments on the bioaccumulation of organometallic compounds in the Tropical Chains

Mercury is a natural component of the earth’s crust and can be released into the environment. In addition to this natural source, there are also various anthropogenic sources. According to a report by the United Nations Environment Programme (2003), industrial activities are responsible for more than 70% of emissions into the atmosphere. Another source of pollution is its use for artisanal gold and silver mining in southern countries. Soils and sediments are recognized as the main storage compartments for mercury in terrestrial and aquatic ecosystems and its transfer to anaerobic aquatic environments can lead to bacterial methylation.

The biomagnification of the methyl mercury thus formed (the most toxic form) and its bioaccumulation along the food chains generate major environmental and health problems, which affect both tropical ecosystems and temperate urban areas. The risks associated with heavy metals in soils and sediments are highly dependent on their speciation and bioavailability, properties that are themselves controlled by the physico-chemical properties of soils, sediments and the action of ubiquitous engineering microorganisms and macroorganisms such as earthworms. Also, the bioavailability of mercury, which is rarely reported in the literature but is crucial to assess its toxicity, will depend on all biotic and abiotic factors capable of modifying its oxidation state as well as the stability of its carrier phases (iron oxides, organic matter).

By choosing mercury as a model contaminant, Guyana as a study site where mercury is a daily reality and a toposequence representative of soil distribution in this region (a continuum from well-draining soils (oxisols) at the top of the slope to a marine sedimentary environment) the INTERCONNECT project is organized around three actions (or worpackages) that propose the following approaches.

WP2 is interested in (1) characterizing the distribution of mercury according to soil and sediment characteristics, (2) identifying potential methylation niches, measuring the bioavailability of mercury WP3 is interested in (1) characterizing the actors of mercury biotransformation (methylation, demethylation, reduction) ; (2) quantify mercury (bio)transformation activities and highlight the role of the different functional groups involved ; (3) measure the in situ response of soil and sediment microorganisms and macro-organisms to the presence of mercurial compounds. WP4 is interested in highlighting the responses to mercury contamination at different cellular and molecular levels in two "macro-invertebrate" study models (earthworms, Chironoma).

This innovative project will therefore seek to highlight the succession of links and processes from a diagnostic stage of mercury in contrasting environments to the impact of its available fraction on the diversity of microbial communities and the physiology of model animals. This interconnection gives a multidisciplinary dimension that has led to the bringing together of specialists from complementary disciplinary fields (Pedology, Geochemistry, Biogeochemistry, Microbial ecology, Molecular ecology). Thus, this project should make it possible to better understand the fate of mercurial compounds, their impact on soil and sediment fauna, and to develop prediction tools concerning the modification of the fate of these contaminants in the sensitive area of French Guiana (and in Amazonia in general) in a global context of direct impacts through human activities and indirect impacts through global change.

– Source, ANR-11-CESA-0020